1. Field of the Invention
The present invention relates to a swirl chamber type Diesel engine and more specifically to such a type of engine wherein the swirl chamber is defined within ceramic inserts which inserts are fitted into a recess formed in an alloy engine cylinder head and which improve the thermal efficiency of the engine by limiting the amount of heat which is lost through the swirl chamber walls.
2. Description of the Prior Art
JM-A-60-171931 discloses a swirl chamber of the nature shown in FIG. 1. This arrangement includes a piston 1 which is reciprocatively disposed in a cylinder 2. The top of the cylinder is closed by a cylinder head 3 in a manner to define a variable volume main combustion chamber 4 therein. The cylinder head 3 is formed with a cavity (no numeral) in which a swirl chamber 5 is defined by a ceramic hot plug 6 and a ceramic dome member 7.
A fuel injector 8 and a glow plug 9 are arranged to project into the swirl chamber through apertures 8a and 9a formed in the ceramic dome member 7.
This arrangement, while limiting the amount of heat which can be transferred to the metallic cylinder head 3 through the ceramic members 6 and 7, has suffered from the drawback that, as the interior of the swirl chamber is exposed to hot combustion gases, the inner surface of the members defining the swirl chamber are induced to develop a very high temperature while, as the amount of heat which is transferred through the ceramic members is relatively small, the temperature of the outer surface, particularly in the case of the dome member 7, is lower than that of the inner one. This produces a temperature differential which induces thermal stress. This stress tends to concentrate in the bridge-like portion of the dome member 7 defined between the openings 8a and 9a, and tends to induce the formation of cracks therein.